1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a method of lifting off and a method of fabricating an array substrate for a liquid crystal display (LCD) device using the same being capable of preventing degrading of image qualities.
2. Discussion of the Related Art
A related art liquid crystal display (LCD) device uses optical anisotropy and polarization properties of liquid crystal molecules. The liquid crystal molecules have a definite alignment direction as a result of their thin and long shapes. The alignment direction of the liquid crystal molecules can be controlled by applying an electric field across the liquid crystal molecules. In other words, as the intensity or direction of the electric field is changed, the alignment of the liquid crystal molecules also changes. Since incident light is refracted based on the orientation of the liquid crystal molecules due to the optical anisotropy of the liquid crystal molecules, images can be displayed by controlling light transmissivity.
Since the LCD device including a thin film transistor (TFT) as a switching element, referred to as an active matrix LCD (AM-LCD) device, has excellent characteristics of high resolution and displaying moving images, the AM-LCD device has been widely used.
FIG. 1 is a plan view showing an array substrate for a related art LCD device. In the LCD device in FIG. 1, both a pixel electrode and a common electrode are disposed on the array substrate. It may be referred to as an in-plane switching (IPS) mode LCD device.
As shown in FIG. 1, the array substrate 10 includes a display region DR and a non-display region NDR at periphery of the display region DR. The display region DR functions as an image display region depending on change of arrangement of liquid crystal molecules. A plurality of gate lines 20 and a plurality of data lines 30 are formed on the array substrate 10. The plurality of gate lines 20 and the plurality of data lines 30 cross each other such that a plurality of pixel regions are defined. Moreover, a plurality of common lines 50 are formed on the array substrate 10. The common line 50 is parallel to and spaced apart from the gate line 20. A common signal is applied to the common line 50 through a common connection line 70 in the non-display region NDR.
If the common connection line 70 is formed of the same layer as the gate line 20, there is a problem of short between the gate lines 20. Accordingly, the common connection line 70 is formed of the same layer as the data line 30. The common connection line 70 is connected to the common line 50 through the common contact hole CMH.
In each pixel region, a pixel electrode (not shown), a common electrode (not shown) and a thin film transistor (TFT) T are disposed. The pixel electrode (not shown) and the common electrode (not shown) are alternately arranged with each other. The TFT T is disposed at a crossing portion of the gate and data lines 20 and 30 and consists of a gate electrode extending from the gate line 20, a semiconductor layer, a source electrode extending from the data line 30 and a drain electrode spaced apart from the source electrode.
A gate pad electrode 42 is disposed at one end of the gate line 20, and a data pad electrode 44 is disposed at one end of the data line 30. The gate pad electrode 42 and the data pad electrode 44 are connected to a gate driving unit (not shown) and a data driving unit (not shown) through a gate tape carrier package (TCP) (not shown) and a data TCP (not shown), respectively. In addition, although not shown, a static electricity protecting circuit line (not shown) and various signal lines are disposed at the non-display region NDR.
The common connection line 70 transfers a common signal from a common signal generating unit (not shown) to a plurality of common lines 50 in the display region DR. Accordingly, the common connection line 70 has a width greater than each common line 50.
On the other hand, to reduce mask process steps, a lift-off method is introduced. However, since various signal lines and metal patterns, for example, the common connection line 70, the gate pad electrode 42, the data pad electrode 44, a static electricity protecting circuit line (not shown), a multi pattern search (MPS) (not shown) line for detecting a short problem and a dummy line (not shown), have a relatively big width, there are some problems in the lift-off method. Particularly, since a stripper for removing a photoresist (PR) pattern with a layer on the PR pattern does not penetrate into a center portion of the above the signal lines and the metal patterns, the PR pattern undesirably remains.
The above problems are explained with reference to accompanied drawings. FIG. 2 is an enlarged plan view of an “A” portion in FIG. 1, and FIGS. 3A to 3C are cross-sectional views showing a fabricating process of a portion taken along the line III-III in FIG. 2. FIGS. 2 and 3A to 3C show the common connection line, while the problems may be also generated in the various signal lines and the metal lines, for example, the gate pad electrode, the data pad electrode, the static electricity protecting circuit line, the multi pattern search (MPS) line and the dummy line in the non-display region.
The line 70 is fabricated by a lifting off process in FIG. 2. Since stripper used for a lifting off process easily penetrates into edge portions D and E of a photosensitive pattern, such as a photoresist (PR) pattern, on the line 70, the photosensitive pattern is perfectly removed. However, it is difficult for the stripper to penetrate into a central portion F. Hereinafter, a photosensitive layer and the photosensitive pattern are referred to as a PR layer and a PR pattern, respectively. Accordingly, the photosensitive pattern remains after the lifting off process. The remaining photosensitive pattern causes a bad effect on following processes or image displaying qualities. When the line has a relative great width, there are serious problems.
The problems of the lifting off process are explained in more detail. As shown in FIG. 3A, a gate insulating layer 45 is formed on a substrate 10. In a non-display region NDR, a metal layer 60 is formed on the gate insulating layer 45, and a PR pattern 82 corresponding to a portion of the metal layer 60 is formed on the metal layer 60.
Next, as shown in FIG. 3B, the metal layer 60 (of FIG. 3A) is etched using the PR pattern 82 as an etching mask to form the line 70 and exposed a portion of the gate insulating layer 45. Since the metal layer 60 (of FIG. 3A) is over-etched, a width of the PR pattern 82 is greater than that of the line 70. Then, a layer 50, for example, a passivation layer, is formed on the PR pattern 82 and the exposed gate insulating layer 45. As mentioned above, since the PR pattern 82 has a greater width than the line 70 due to over-etching, there are discontinuation in the layer 50 at boundary portion between the PR pattern 82 and the line 70.
Next, as shown in FIG. 3C, the stripper is penetrated into the discontinuous portion of the layer 50 to perform a lifting off process. As a result, the PR pattern 82 and the layer 50 directly on the PR pattern 82 are removed at the same time. In this case, since the stripper easily penetrates into edge portions D and E of the line, the PR pattern 82 and the layer 50 directly on the PR pattern 82 at the edge portions D and E are perfectly removed. However, the stripper is difficult to be penetrated into a central portion F of the line 70, the PR pattern 82 and the layer 50 directly on the PR pattern 82 at a central portion F is scarcely moved. The PR remaining PR pattern 82 causes a bad effect.
On the other hand, there are first to fourth non-display regions in the array substrate. For example, the gate pad and the data pad are formed in the first and second non-display regions, respectively. When a material layer of a pixel electrode is formed in the third and fourth regions, there are some problems such as a short on adjacent pixel regions and corrosion. However, since the non-display regions have a relatively greater width, a PR pattern and the material layer of the pixel electrode remain such that image displaying qualities are degraded.